1. Technical Field
The present invention relates to a printing apparatus that includes an ink circulation path having the ink discharge head.
2. Related Art
Recently, an ink jet printer, which includes a print head that discharges ink, a sub-tank that stores ink, a supply pump that supplies ink to a sub-tank from a main tank containing the ink, and a circulation path having a forward path through which the ink, which is supplied from the sub-tank to the print head, flows, and a backward path through which the ink, which returns to the sub-tank from the print head, flows, has been known (refer to JP-A-2012-183695).
The inventors have found the following problems.
In the printing apparatus such as an ink jet printer in the related art, a height difference between the nozzle surface of the ink discharge head and a level of the ink in the ink storage unit becomes a water head difference which has an influence on a back pressure (hereinafter, referred to as a “head back pressure”) of the ink in the ink discharge head. In order to control fluctuation of the head back pressure, a level of the ink stored in the ink storage unit may be positioned within a predetermined height range. Therefore, it is preferable that a liquid sending unit supplies the ink from the ink container to an ink storage unit depending on an ink discharge amount from the ink discharge unit. However, the level of the ink in the ink storage unit becomes lower than a predetermined range, in some cases, such as when the ink is not properly supplied to the ink storage unit due to an abnormality in the liquid sending unit. In this case, since the height difference between the nozzle surface of the ink discharge head and the level of the ink in the ink storage unit, that is, the water head difference which has an influence on the head back pressure becomes greater, the head back pressure fluctuates.